Chemical and physical parameters as quality indicators of used frying fats

There are many methods available in the literature to test the physical properties and chemical changes of frying fats. Physical methods include density, viscosity, smoke point, colour, refractive index, ultraviolet (UV) absorption, infra-red spectroscopy, and dielectric constant. Chemical tests are the determination of free fatty acids (acid value), iodine value, anisidine index, saponification value, non-oxidised monomer fatty acids, polymerised triglycerides, fatty acids insoluble in petrol ether, and total polar compounds. Quality control in the production of fried food, whether the analyst is a quality control inspector or a member of the health food inspection service, demands a simple, easy procedure, using no chemicals. The results should correspond to official methods such as polar compounds. Among all physical and chemical methods, the determination of polar materials, polymerised triglycerides by size exclusion chromatography (HPSEC), and acid value were selected to be compared with the results of the measurements of the dielectricity constant (Food Oil Sensor) and the relative viscosity and density (Fri-Check®,respectively. More than 150 samples, taken in commerce by the food inspection, were analysed and statistically evaluated.